<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        canvas {
            border: 1px solid red;
        }
    </style>
</head>

<body>
    <canvas width="500" height="500" id="mycanvas"></canvas>

    <script>
        let canvas = document.querySelector("#mycanvas");
        //获取上下文:画笔
        let context = canvas.getContext("2d");
        //预加载:等待资源加载完毕之后再使用
        function loadImg() {
            return new Promise((resolve, reject) => {
                // let img = new Image();
                let img = document.createElement("img");
                img.src =
                    "https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.jj20.com%2Fup%2Fallimg%2Ftp02%2F1Z9191923035R0-0-lp.jpg&refer=http%3A%2F%2Fimg.jj20.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1661397561&t=a620034e48d31890e7e652561c79083b"

                img.onload = function () {
                    resolve(this);
                }

                //图片加载失败
                img.onerror = function () {
                    reject("图片加载失败");
                }
            })
        }

        loadImg().then(img=>context.drawImage(img,50,50,300,300),err=>console.log("error",err));
    </script>
</body>

</html>